Lost Definition and 576 Threads

  1. D

    Is it a scalar product? I'm kind of lost

    The Vector A points 17° counterclockwise from the positive x axis. Vector B lues in the first cuadrant of the xy plane. The magnitudes of the cross product and the dot product are the same: i.e, |AXB|= |A(times)B| What Angle does B make with the positive x axis? 2. Is ti a scalar...
  2. R

    How Much Kinetic Energy is Lost

    Homework Statement A 2.00-kg object traveling east at 20.0 m/s collides with a 3.00-kg object traveling west at 10.0 m/s. After the collision, the 2.00-kg object has a velocity 5.00 m/s to the west. How much kinetic energy was lost during the collision? (no image was given). Homework...
  3. D

    Lost My Mojo: How Can I Regain My Academic Motivation?

    Hey I am doctorwes and I am a A2 student in Maths, Physics and ICT Recently, I have been feeling rather cr*p towards my work in both Maths and Physics. I mananged to get a B in our maths assessment, on which I should have got 90 percent or more and now I have got my physics paper back and I...
  4. A

    Finding heat lost when waters of different temps. Are mixed

    Homework Statement 90 grams of water at 75°C are mixed with an equal amount of water at 25°C in a completely insulated container. The final temperature of the water is 50°C. How much heat is lost by the hot water? Homework Equations The hot water drops to 50 degrees Celsius so it has...
  5. V

    Inelastic collision in opposite directions: KE lost & angular momentum

    1. The problem statement. Two boys are sliding toward each other on a frictionless, ice-covered parking lot. Jacob, mass 45 kg, is gliding to the right at 7.98 m/s, and Ethan, mass 31.0 kg, is gliding to the left at 10.7 m/s along the same line. When they meet, they grab each other and hang on...
  6. Y

    Circular Motion and Oscillationshave been sick and am lost

    Homework Statement A particle begins at rest on a circular track and is subjected to a constant angular acceleration of magnitude α beginning when t=0s.(a) Show that the magnitudes of the tangential and centripetal accelerations of the particle are equal when t=(1/α )^(1/2) Independent...
  7. L

    Exploring Career Options in Medical Physics and Beyond: What You Need to Know

    I have recently posted about trying to enter a masters/phd program for Medical Physics (Going to try for SDSU and LSU). Before this week i was quite hopeful and naive i suppose. I was not aware of how tough the job market was and the bottlenecking in the residency programs. Don't get me...
  8. A

    Probability/Statistics (really lost)

    I'm not a native English speaker, and this assignment wasn't originally in English, so I had to translate it to English, thus the grammar errors, but hopefully it's understandable) ----------------------------------- For an investment in an equity assessed in general to be the following...
  9. P

    Electrodynamics Potential from charged sphere. I am lost :/

    ~Electrodynamics~ Potential from charged sphere. I am lost :/ Homework Statement A sphere of radius R, centered at the origin, carries a charge density ρ(r,θ)=κ/r^2(R-2r)sin^2(θ). κ is constant. Find exact potential. Homework Equations 1/4∏ε∫ρ∂t/r The Attempt at a Solution Question and...
  10. N

    Calculate the cost of the energy lost to heat per hour per meter

    Homework Statement A small city requires about ##17 \mbox{MW}## of power. Suppose that instead of using high-voltage lines to supply the power, the power is delivered at ##120 V##. Assuming a two-wire line of 0.60cm -diameter copper wire, estimate the cost of the energy lost to heat per hour...
  11. G

    Mass Lost by the Sun by emitting radiation

    Hi, I recently did a homework problem for my introductory Quantum Mechanics course and in the problem we were given the sun's temperature in Kelvin as well as the diameter of the sun and instructed to calculate the rest mass lost per second to radiation by the sun. I was able to solve the...
  12. 7

    FINITE potential step - SOS - got lost in system of equation

    Homework Statement Homework Equations I know that energy mentioned in the statement is kinetic energy so keep in mind when reading that ##E\equiv E_k##. In our case the kinetic energy is larger than the potential energy ##\boxed{E>E_p}## and this is why stationary states for the regions 1...
  13. jfizzix

    How is the energy of an electron lost in a classical hydrogen atom?

    Consider the following. You have an electron of negative charge orbiting a proton of positive charge at some distance R (i.e. a classical hydrogen atom). I understand the hydrogen atom is unstable under classical physics because the accelerating electron loses its kinetic energy as...
  14. W

    About different Green functions, I'm lost

    Hello everyone:(Please forgive my poor English.) I've been learning many-body theory for a year or so, however, I'm quite confused with different Green's functions (GF) there. One of the most things I want to get clear is about zero-temperature GF and imaginary-time GF (or Matsubara GF), both...
  15. Nugso

    Navigating My Future: My Journey from Engineering to Mathematics and Physics

    Hello everyone. Before I start asking my question, I'd like to, if I may, talk about myself. I'm currently studying Aeronautical/Aerospace engineering and the following year will be my third year(including undergraduate preparotry). But, I don't really want to be an engineer, but a mathemetician...
  16. H

    Heat gained and lost by aluminium and water in thermal equilibrium

    Homework Statement A physicist pours 100g of water at 100'C into a 20g aluminium cup which already contains 50g of water at 20'C. The final equilibrium temperature of the water is 71.847. C(water)=4186J/kgC C(aluminium)=900J/kgC 1. the amount of heat lost by the hot water 2. the amount...
  17. R

    Find eccentricity of orbit after star has lost mass

    Homework Statement Initially, a planet with mass m moves on a circular orbit (r = R) around a star with mass M. Now M is instantaneously decreased to M'. Find the eccentricity e of the elliptical orbit the planet now follows. Homework Equations specific angular momentum l = L/m...
  18. Andre

    What caused the mysterious disappearance of the Lost City of Heracleion?

    This thread is a present for Evo's birthday :smile: There was some media coverage of Heracleion here and here the other day. Check out the links, awesome photo's. However the global sea level rise in the last 3000 years was maybe three feet, so only 15 feet would be accounted for...
  19. A

    Amount of Kinetic Energy Lost in Inelastic Collision

    1. Two carts, each of mass M, travel towards each other on a frictionless air track, one with velocity V, and the other with -3V. They collide and stick together. How much kinetic energy is lost in the collision? 2. P = mv, KE=1/2mv2 3. Initial KE of the system is the sum of the kinetic...
  20. Evo

    News US banks to send checks to 4.2M who lost homes

    Finally, something being done for homeowners that lost their homes without proper evaluation. http://news.yahoo.com/us-banks-send-checks-4-153752525.html
  21. X

    How do I find energy lost? Something very simple is confusing me

    Homework Statement Find the kinetic energy lost Homework Equations The Attempt at a Solution We solved it in class Ek1 = -206 J Ek2 = 10 J Find the energy lost. The answer is was 2.2 * 10^2 J lost This is confusing for me, to find energy lost, we should subtract the...
  22. B

    Calculating lost mechanical energy

    Hey guys, I'm trying to complete a homework problem, but I'm not quite sure how to approach it. Here is the question: A 90.5-kg fullback running east with a speed of 4.91 m/s is tackled by a 94.7-kg opponent running north with a speed of 2.93 m/s. Determine the mechanical energy that...
  23. I

    Electric Current: Finding Energy lost in a capacitor

    Homework Statement E& M Purcell, 3.11 A 100-pF capacitor is charged to 100 volts. After the charging battery is disconnected, the capacitor is connected in parallel to another capacitor. If the final voltage is 30 volts, what is the capacitance of the second capacitor? How much energy...
  24. W

    Lost physics student problem with vectors

    Homework Statement These are two problems my professor has given me to do. I'm not very good at physics and could use a little help. 1. Sir Killalot's foe Dead Metal is due north of Sir Killalot's position and at a distance of 12m. Dead Metal moves 15m at an angle of 30 degress to a new...
  25. C

    The paradox of lost energy details below?

    Imagine two bodies A & B. they have same mass and same speed, but they are traveling in different direction. the kinetic energies of both the bodies is equal (1/2*mv^2), because they have same speed and mass. now they collide each other. As they have same mass and speed they both stop. now the...
  26. H

    How much energy is lost due to neutrinos in matter-antimatter reaction ?

    I read that matter-antimatter annihilation is not as useful as we thought because a large amount of energy is carried away by neutrinos. So, how much is this energy ? What is the percentage of the lost energy to the energy calculated from E=mc^2 ?
  27. F

    Find the energy lost at the collision and the average force of friction

    Homework Statement We have to make a roller coaster for our school project. This coaster starts with a spring. In this coaster, there is a collision. Essentially, I need to find the energy lost at the collision, and the average force of friction. Homework Equations Em1=Em2 W=Fd F=ma A=DELTA v/...
  28. I

    Is all electrical energy eventually lost as heat in solid state electronics?

    I've never heard it said before but it appears to me that all electrical current that flows in a solid state component system; processors, diodes, transistors, resistors, etc. is eventually dissipated as heat. What are your thoughts about this?
  29. J

    The lost energy of Cosmic Background Radiation

    Could anyone clarify where is gone the energy lost by CBR as the universe expands? Thank you in advance and happy new year
  30. L

    Is Burnout Inevitable for Physics Students Pursuing Astrophysics Research?

    I'm a 4th year physics student in the EU. Over the course of my undergrad degree I developed an unbalanced lifestyle to pull through the degree and learn as much as I could, with hopes of going to graduate school to do astrophysics research. I gave up on regular exercise and hobbies in my 2nd...
  31. E

    Mass lost in a single fusion reaction

    How much mass is lost in a single D + T= 4He fusion reaction? And is all of the mass lost converted to energy or just some? The mass lost can be converted to energy using e=mc2.
  32. C

    Advice for a lost wanna-be physicist

    Hello all, I'm new here. I'm at a point in life and in school where it's difficult to discern where I'm heading and what I should expect out of myself academically and professionally in the next few years. I'm 23 years old and I didn't realize until the age of 21 what it was that I was...
  33. Y

    How to recover lost folder in the flash drive ( USB stick)?

    My wife lost a file that she worked directly from a flash drive. Somehow, the whole folder disappeared. Is there any way to recover that folder? Problem is she did not work off the C drive where even you accidentally deleted it, you can find it in the trash bin. She worked directly off the...
  34. V

    Infinite Geometric Sequence: How to Find the Number of Terms

    Homework Statement How many terms are in each sequence? 12, 4, 4/3, ..., 4/729 Homework Equations The Attempt at a Solution using tn=t1(r)(n-1) ? I am lost
  35. T

    Kinetic energy: what percentage has been lost?

    Homework Statement So there's a particle of mass 4u that strikes another particle of mass 196u. The collision is elastic. What percentage of its original kinetic energy has the moving particle lost? Homework Equations m1v1o + m2v2o = m1vf + m2v2f K1o + K2o = K1f + K2f The Attempt...
  36. L

    Finding the energy lost in a collision as the bullet collides to the block

    Homework Statement a 50 g bullet hits and becomes embedded in a wooden block of as 450 g which is at rest on a surface (μ = 0.41) and is attached to a spring bumper. The block and bullet compress the spring bumper a distance of 20 cm. Is the spring constant is 250 N/m find initial speed of...
  37. C

    Magnetic force lost when you break a magnet?

    if you have a magnet that pulls 40lbs of force if you broke that into 2 how much force will each magnet pull. i have some neodymium magnets from hardrives and i want to break them up but i want to know if that's gunna make them lose a lot of force. anyone know the formula for calculating...
  38. P

    Find mechanical energy lost when a cyclist goes down a hill

    A cyclist has a speed of 5 m/s when she beings to coast down a hill, as shown in the figure. At the bottom of the hill, her speed has increased to 12m/s. the mass of the cyclist plus bicycle is 75kg. a) Calculate the work done by gravity on the cyclist and bicycle. b) Calculate the...
  39. Z

    Introductory Bohrs Model Problem and I'm Lost

    Introductory Bohrs Model Problem...and I'm Lost! Ok, so I "think" what I am trying to find here is the frequency of the energy between two states of energy. I admit that part of my problem probably lies in the fact that I'm not even sure what it is I'm trying to find. My class seems to be just...
  40. A

    What are the different types of infinities?

    How can there be different types of infinities? I just learned that cardinality of set of natural numbers, integers, prime numbers is alepho. Why are we replacing infinity with a number i.e. alepho. And what further blows my mind is that cardinality of real numbers is also infinity but a...
  41. N

    I'm LOST Car is suppose to overtake truck but at what velocity?

    I'm LOST! Car is suppose to overtake truck but at what velocity? two cars C and D move in the same direction in parrallel lanes of a straight road. C starts from rest and begins to move with a constant acceleration. at that instat the C begins to move it is overtaken by D, which is moving with...
  42. N

    Find the Current After the Capacitors Have Lost 80% of Stored Energy

    Homework Statement In the circuit shown in the figure each capacitor initially has a charge of magnitude 3.00nC on its plates. A) After the switch S is closed, what will be the current in the circuit at the instant that the capacitors have lost 80.0% of their initial stored energy...
  43. B

    Is information lost if a particle is annhilated by it's antiparticle

    If a particle (let's call it Z) is happily minding it's own business, and a particle-antiparticle pair spawns in it's vicinity (let's call them particle A and B, created from 'zero point' energy), and it just so happens that the antiparticle (let's say B) collides with particle Z before it is...
  44. nukeman

    So lost on exact trig ratio questions Please help

    Homework Statement I am reviewing some trig, and I forgot how to do this. Please let me figure this one simple thing out. Here is the questions. Find the exact trig ratios of 5∏/6 Ok, now look at my diagram below to see where I am having trouble with! What simple process am...
  45. N

    How to Calculate Energy Lost in a Rolling Sphere?

    Homework Statement There is a tube attached to a board in a fashion that a ball can be dropped in the top and the tube curves to the right 90°. If a ball of mass 7.6g is dropped into the top of the tube, what is the minimum height the exit point of the tube needs to be in order for the ball to...
  46. E

    Calculating Light Signal Velocity: Relativistic Effects at 0.5c

    Homework Statement You fire a light signal at 60° north of west. (a) find the velocity components of this signal according to an observer moving eastward relative to you at 0.5c. From them, determine the magnitude and direction of light signal's velocity according to the other observer. (b)...
  47. E

    A Twin Paradox Question, totally lost.

    Homework Statement Planet W is 12ly from earth. Anna and Bob are both 20 years old. Anna travels to planet W at 0.6c, quickly turns around, and returns to Earth at 0.6c. How old will Anna and Bob be when Anna gets back? Homework Equations The Attempt at a Solution I've tried...
  48. N

    Heat lost from face due to black body radiation

    Homework Statement Much of the of heat lost from a cross-country skier's body is radiated from the head, since it is often uncovered. Treat a head as a 20-cm-diameter, 20-cm-tall cylinder with a flat top. If the surface temperature of a body is 35 C, what is the net rate of heat loss on a...
  49. Y

    Understanding Linear Algebra: Span of Vectors in R^4 Explained

    [b]1. i am given a matrix A= 1 0 2 1 1 1 3 1 2 3 8 -2 -3 3 -5 1 and then it asks why do I know that span {a1, a2, a3, a4} are a subset of R^4. Homework Equations The Attempt at a Solution Is it as easy as saying "because there 4 vectors?"
  50. turbo

    We lost Michael Clarke Duncan today.

    He had a heart attack a month or so ago, and complications got him. You might remember him as the "gentle giant" in the film "The Green Mile". He played that part so well... RIP
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